1. Field of the Invention
An aspect of this disclosure relates to a charge circuit.
2. Description of the Related Art
Portable terminals driven by a secondary battery such as a lithium-ion battery are widely used. U.S. Pat. No. 7,548,041, for example, discloses a charge circuit for charging a secondary battery of a portable terminal. The charge circuit includes a charge timer to ensure safety.
FIG. 1 is a circuit diagram illustrating a related-art charge circuit. A charge circuit 10 illustrated in FIG. 1 includes an IN terminal receiving a current (charge current) from an AC adapter and a BAT terminal connected to a secondary battery. The charge circuit 10 also includes a switching element M1 for stopping charging and a charge timer 11. In the charge circuit 10, the secondary battery connected to the BAT terminal is charged by a current input from the IN terminal. Also in the charge circuit 10, a predetermined clock number is set in the charge timer 11. When the number of counted clock pulses reaches the predetermined clock number, the switching element M1 is turned off to shut off the charge current and stop the charging.
FIG. 2 is a circuit diagram illustrating another related-art charge circuit. A charge circuit 20 illustrated in FIG. 2 includes in addition to an IN terminal and a BAT terminal, an OUT terminal that outputs a current input from the IN terminal. The current output from the OUT terminal is supplied to a portable terminal driven by a secondary battery as an operating current.
In the related-art charge circuit 20 of FIG. 2, the current input from the IN terminal is divided into a current that flows to the OUT terminal and a current (charge current) that flows to the BAT terminal. Accordingly, with this configuration, the level of the charge current flowing to the BAT terminal may sometimes be decreased. Even in such a case, however, charging is stopped by a charge timer 21 when a predetermined period of time passes. As a result, the secondary battery may be insufficiently charged.
To prevent charging from being stopped while the battery charge is insufficient, the clock number set in the charge timer 21 may be increased to increase the predetermined period of time. However, increasing the predetermined period of time may reduce the safety the charge timer 21 is intended to provide.